Vitamin D is essential for bone health. Bone growth is high during childhood and adolescence. So it may be especially important to identify and treat vitamin D deficiency during that time, the researchers write.

Previous research suggests that obesity may put you at risk for vitamin D deficiency.

Overweight Kids and Vitamin D

Researchers in the study analyzed data from more than 12,000 U.S. children and teens aged 6 to 18. The children were enrolled in the 2003-2006 National Health and Nutrition Examination Survey.

About 21% of the healthy-weight youngsters were deficient in vitamin D. That was also true for 29% of those who were overweight, 34% of those who were obese, and 49% of those who were severely obese.

Even after accounting for such factors as vitamin D supplementation and intake of milk, which is typically fortified with vitamin D, the rates of vitamin D deficiency were higher in Latinos and African-Americans. Among the severely obese youngsters, 27% of whites, 52% of Latinos, and 87% of African-Americans were deficient in vitamin D.

"The particularly high prevalence in severely obese and minority children suggests that targeted screening and treatment guidance is needed," the researchers conclude.

Researcher Christy Turer, MD, a pediatrician at the University of Texas Southwestern Medical Center and Children's Medical Center in Dallas, says she and her colleagues already were routinely checking vitamin D levels in children at specialty clinics, such as weight management clinics. Those found to be deficient are prescribed high-dose vitamin D supplements, a pill taken weekly. After eight weeks of treatment, their levels are rechecked, and if they're near normal, she'll cut them back to monthly doses of vitamin D supplements.

Turer also recommends that vitamin-D-deficient patients drink low-fat milk. If they don't like to drink plain milk, she says they can add artificially sweetened flavors that add only 15 calories a serving.

"The reason that milk is important is it has not just vitamin D, but it has calcium," she says. Unsweetened soy milk and almond milk are also good sources of vitamin D and calcium, Turer says.

Go Outside and Play

Turer says overweight, vitamin-D-deficient children should walk away from the television or computer screen and go outside and move around. That's because the sun is one of the main sources of vitamin D.

It's not known whether children get as much vitamin D from the sun as adults, she says. Turer suggests that children should get 10 or 15 minutes of sun before putting on sunblock.

Parents who think their child might be deficient in vitamin D should talk to their doctor before giving them supplements that are available without a prescription, Turer says. "There are risks from taking too much vitamin D."

Checking the blood level of vitamin D costs about $100.Turer says more research is needed to determine whether routine screening is cost-effective and whether treating deficiencies reduces the risk of fractures and other related health problems.

Earlier Research on Vitamin D

Recent, smaller studies of children in Somerville, Mass., and Charleston, W.Va., reached similar conclusions.

Tufts researchers evaluated 145 fourth- through eighth-graders. More than 83% of the children were found to be vitamin D deficient. Researcher Lauren Au, RD, says that high levels of vitamin D deficiency may be partly explained by the fact that more than half of them were overweight or obese. Also, Au says, their Vitamin D levels were checked during the winter, when sun exposure is lower.

In another small study, Stephen Sondike, MD, an adolescent medicine specialist at West Virginia University, compared vitamin D levels in 76 patients aged 2 to 18. The patients had a diagnosis of obesity, chronic kidney disease, diabetes, high blood pressure, or cystic fibrosis. Only obesity was associated with vitamin D deficiency.

Sondike, medical director of the Disordered Eating Center of Charleston, says he routinely checks the vitamin D levels of overweight and obese patients. The notion that such children are malnourished might seem counterintuitive, he says, but "their diet is heavy in calories and not heavy in nutrients."